Up to 50 centers using Vantas, the recently approved histrelin implant as part of their urology practice for treating patients with advanced prostate cancer, were to be identified for participation in this Phase IV post-marketing trial. Up to 10 patients who had been implanted with Vantas at these participating centers, and who had difficult to locate or non-palpable implants at the time of removal, were to be enrolled in this trial. A Screening Visit was to be conducted to consent the patient and to collect basic medical and safety information for patient participation. Upon patient enrollment, up to three subsequent Visits (Visits 1, 2, and 3) were to be conducted (within 2 weeks of the Screening Visit). The investigator was to locate and remove the implant by following the instructions provided in the protocol. Methods for location of the implant included ultrasound, CT, or MRI procedures. The visit at which the implant was successfully located and removed was to be the final study visit for the patient. Upon successful retrieval of the implant or a determination that, per Study Instructions, the implant cannot be located/removed, the study was completed for the patient. No information was to be collected on re-implantation of a new implant. Safety was to be monitored throughout the two week study. Blood samples for testosterone and PSA were only collected at the Screening Visit. The implants removed from the patients were to be returned to Indevus Pharmaceuticals for analysis.